1. Field of the Invention
The present invention relates to an electronic imaging device such as a digital camera, and in particular relates to an imaging device and imaging method capable of generating a bulb exposure image with relatively bright composition, and capable of arbitrary exposure adjustment.
2. Description of the Related Art
Conventionally, with a single lens reflex type imaging device observing a subject image has been performed using an optical viewfinder. However, imaging devices for observing a subject image not through an optical viewfinder but by live view display for displaying an image that as been read from an image sensor using a rear surface liquid crystal monitor or the like have recently become available on the market. Also, instead of an optical view finder, imaging devices have also become available on the market that display an image through live view display using an electronic view finder that is separate from a rear surface liquid crystal monitor, and are capable of switching between display using the above described rear surface liquid crystal monitor and display using the electronic viewfinder.
Conventionally, regardless of whether an optical view finder or an electronic viewfinder is used, at the time of a prolonged exposure, such as with a bulb exposure, it was not possible to read image data from the image sensor during exposure, which meant that it was not possible to confirm the state of the subject or exposure conditions, and an image was only confirmed upon completion of shooting. As a result, for the photographer setting of exposure values such as aperture and ISO sensitivity, and deciding when to start and stop the exposure, need to be decided by the photographer themselves confirming from subject brightness etc., and it is not an easy matter to obtain a desired image without having an exposure ruined due to insufficient exposure or over exposure.
In order to address this type of drawback, therefore, the imaging device disclosed in Japanese patent laid-open No. 2005-117395 (hereafter referred to as patent literature 1) reads image data from an image sensor at specified time intervals, carries out simple cumulative addition of image data every time that this image data is read out from the image sensor, and displays an image obtained in this way on a liquid crystal monitor or the like, so as to be able to display the course of exposure.
Also, with the imaging device disclosed in Japanese patent No. 4148586 (hereafter referred to as patent literature 2), image data is continuously read out from an image sensor, and bulb exposure image data is generated with relatively bright composition. This relatively bright composition is image composition where brightness levels for every pixel of image data are compared, and those with large brightness are selected to give a brightness level after composition.
With the imaging device disclosed in patent literature 1, it is possible to notify current exposure information to the photographer during a bulb exposure as progression information, and it is possible to alleviate failures such as under exposure and over exposure. However, a subject for bulb exposure is generally shooting light trails of fireworks launched into the night sky or light trails of stars, and as well the length of light trails becoming longer with increased exposure time, there are variations in brightness of the background (the night sky in these cases). In this type of situation, it is necessary to complete the exposure in an exposure time that ensures that the brightness of the background is not over exposed or under exposed, and the length of light trails will be determined by the brightness of the background regardless of the artistic intentions of the photographer.
Contrary to this, with the imaging device disclosed in patent literature 2, for image data that is read out continuously from the image sensor, brightness levels are compared for every pixel of the image data, and brighter pixels are selected and set for the brightness level after combination, to generate taken image data of relatively bright composition. Therefore, regardless of exposure time, brightness of a background will be maintained at the brightness of a single image before combining, and it is possible to trace light trails by setting an exposure time in line with the creative intentions of the photographer.
However, with either of the imaging devices of patent literature 1 or 2, when the photographer shoots as intended in accordance with background brightness and light trace length, respectively, it is necessary to adjust aperture and ISO sensitivity to match subject brightness, and to adjust exposure time for shooting a single image before combination. This adjustment requires long years of photography experience or confirmation of brightness using preview, and requires advanced shooting technology.
Also, in order to carry out shooting in a dark environment, such as stars and fireworks, if an image is confirmed in a bright environment such as in the daytime or indoors, then in order for a taken image to appear at a brightness that is different to that at the time of shooting, shooting will often be carried out at a brightness that does not conform with the shooting intention.